Substrate processing method

ABSTRACT

In a substrate processing method for etching a silicon oxide layer formed on a surface of a substrate, a surface of the silicon oxide layer is hydrophilized. Then, the silicon oxide layer is etched by supplying a halogen-containing gas to the substrate and sublimating a reaction product generated by reaction between the halogen-containing gas and the silicon oxide layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is National Stage Application of the PCT ApplicationNo. PCT/JP2017/004431, filed on Feb. 7, 2017, entitled “SubstrateProcessing Method,” which claims priority to the Japanese PatentApplication No. 2016-030365 filed on Feb. 19, 2016. The entire contentsof the foregoing applications are incorporated herein by reference forall purposes.

FIELD OF THE INVENTION

The present invention relates to a substrate processing method forperforming etching by supplying a processing gas to a surface of atarget substrate.

BACKGROUND OF THE INVENTION

Along with diversification and three-dimensional development ofsemiconductor devices, the structures of the devices become complicatedand miniaturized. Therefore, even in each process of a semiconductormanufacturing process, it is required to deal with various new surfacestructures and film types. For example, a process of fabricating atransistor of a three-dimensional structure includes a step of formingan SiO₂ (silicon oxide) film that is an insulating layer for separatingtransistors, which includes precursor structure portions of thetransistors, and then etching the SiO₂ (silicon oxide) film until theprecursor structure portions are exposed.

As for a method for etching an SiO₂ film, there is known a method usinga chemical oxide removal process by HF (hydrogen fluoride) gas and NH₃(ammonia) gas as disclosed in, e.g., Japanese Patent ApplicationPublication No. 2009-156774. In this method, HF gas and NH₃ gas aresupplied into a processing chamber to etch an SiO₂ film formed on asurface of a semiconductor wafer (hereinafter, referred to as “wafer”).These gases react with SiO₂ to generate (NH₄)₂SiF₆ (ammonium siliconfluoride). (NH₄)₂SiF₆ thus generated is sublimated by heating the waferin the same processing chamber. As a result, SiO₂ is removed.

When the miniaturization of a circuit pattern progresses, in an SiO₂film for insulating transistors, a degree of roughness on the surface ofthe SiO₂ film greatly affects leak characteristics. Therefore, there isa demand for improving the surface roughness of the SiO₂ film.

Japanese Patent Publication Application No. 2003-68766 discloses atechnique of performing plasma processing using plasma obtained byactivating O₂ to improve wettability for etching at the time of removingan oxide film formed on a surface of a substrate. However, in thistechnique, the surface roughness after etching is not considered.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a technique capableof suppressing deterioration of roughness at the time of etching a partof an SiO₂ layer formed on a surface of a substrate.

In accordance with an aspect of the present invention, there is provideda substrate processing method for etching a silicon oxide layer formedon a surface of a substrate. The substrate processing method includes: afirst step of hydrophilizing a surface of the silicon oxide layer; and asecond step of etching the silicon oxide layer by supplying ahalogen-containing gas to the substrate and sublimating a reactionproduct generated by reaction between the halogen-containing gas and thesilicon oxide layer.

In the present invention, when the silicon oxide layer formed on thesurface of the substrate is etched, the silicon oxide film is etched bya halogen-containing gas after the surface of the silicon oxide layer ishydrophilized. Therefore, the surface of the silicon oxide layer isuniformly etched, and the surface roughness is improved. This mechanismwill be described later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional perspective view showing a vicinity of asurface of a wafer before etching.

FIGS. 2 and 3 explain an etching state on the surface of the wafer.

FIG. 4 is a cross sectional perspective view showing the surface of thewafer and therearound after the etching.

FIG. 5 is an explanatory view schematically showing the surface of thewafer before the etching.

FIGS. 6 and 7 are explanatory views schematically showing the surface ofthe wafer after oxygen radical treatment.

FIG. 8 explains an etching state on the surface of the wafer.

FIG. 9 is a cross sectional view showing a radical treatment apparatusfor supplying oxygen radicals to the wafer.

FIG. 10 is a cross sectional view of a COR treatment apparatus foretching an SiO₂ film by COR.

FIG. 11 is a top view showing a vacuum processing apparatus.

FIG. 12 is a characteristic diagram showing a root mean square roughnessin a test example, a comparative example and a reference example.

FIG. 13 shows images of the surface of the wafer in the test example,the comparative example and the reference example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An example of a surface structure of a wafer W that is a targetsubstrate to be processed by a substrate processing method according toan embodiment of the present invention will be described. FIG. 1 shows asurface structure of the wafer W during a semiconductor devicemanufacturing process. In this surface structure, a plurality ofprotruding walls 11 extending in parallel to each other is formed byetching an Si (silicon) layer 10. A groove 12 is formed between theprotruding walls 11 adjacent to each other. An SiO₂ thermal oxide film(first SiO₂ film) is formed on the entire surface of the wafer Wincluding inner surfaces of the grooves 12 by heating the wafer W in anoxidizing atmosphere. Then, a second SiO₂ film 14 is formed on theentire surface of the wafer W including the inner surfaces of thegrooves 12 by, e.g., CVD (Chemical Vapor Deposition) using an organicraw material gas and an oxidizing gas.

Next, the second SiO₂ film 14 is treated at high temperature byperforming annealing for heating the wafer W at 400° C. to 1000° C.while performing purging by using N₂ gas in a vacuum atmosphere.Thereafter, the surface of the wafer W is polished by CMP (ChemicalMechanical Polishing). Accordingly, upper surfaces of the protrudingwalls 11 are exposed on the surface of the wafer W. FIG. 1 is a crosssectional perspective view showing a surface structure of a wafer Wafter polishing. In FIG. 1, a thickness of the first SiO₂ film 13 isillustrated in an exaggerated manner. Since, however, the first SiO₂film 13 is thin and thus is hardly exposed on the surface. In thefollowing specification, the first SiO₂ film 13 and the second SiO₂ film14 are illustrated as an SiO₂ film 1. In an embodiment of the presentinvention, the SiO₂ film 1 corresponds to a silicon oxide layer.

Next, the wafer W is transferred to a radical treatment apparatus, andoxygen radicals 102 are supplied to the surface of the wafer W.Specifically, there may be employed, e.g., a method for supplying plasmaobtained by activating O₂ (oxygen) through an ion trap plate, as will bedescribed later.

Then, the wafer W is transferred to a known COR (Chemical Oxide Removal)treatment apparatus. The SiO₂ film 1 is etched by a COR method forremoving the SiO₂ film 1 by reaction between the SiO₂ film 1 and HFmolecules 104 and NH₃ molecules 105. In the COR treatment apparatus, HFgas and NH₃ gas are supplied to the wafer W as will be described later.Accordingly, the HF molecules 104 and the NH₃ molecules 105 are adsorbedon the surface of the SiO₂ film 1.

When the HF molecules 104 and the NH₃ molecules 105 are adsorbed on thesurface of the SiO₂ film 1, the SiO₂ film 1 reacts with the HF molecules104 and the NH₃ molecules 105 as shown in FIG. 2 to generate a reactionproduct 106, e.g., (NH₄)₂SiF₆, water, and the like. By heating the waferW to, e.g., 115° C., the reaction product 106 such as (NH₄)₂SiF₆, water,and the like are volatilized (sublimated) and removed as shown in FIG.3. Thereafter, the supply of the NH₃ gas and the HF gas is stopped and apurge gas is supplied to flow. Accordingly, the sublimated reactionproduct such as (NH₄)₂SiF₆, water, and the like are exhausted by thepurge gas, and unreacted HF molecules 104 and unreacted NH₃ molecules105 are removed by the purge gas. Therefore, the reaction between theSiO₂ film 1 and the HF molecules 104 and the NH₃ molecules 105 isstopped, and the etching is stopped. As a result, the SiO₂ film 1 thathas become the reaction product 106 is removed and the etching isperformed to leave the SiO₂ film 1 in the grooves 12 as shown in FIG. 4.

By supplying oxygen radicals to the SiO₂ film 1 before the etching ofthe wafer W having the SiO₂ film 1 using the COR method, roughness isimproved as can be seen from a test example to be described later.

The reason for improvement of the roughness is presumed as follows. Onthe surface of the SiO₂ film 1 of the wafer W that has been subjected tothe CMP shown in FIG. 1, most of hydroxyl groups (OH groups) 101 areremoved by at least one of annealing and CMP, and dangling bonds 100 ofSiO₂ molecules are arranged as shown in FIG. 5.

Thereafter, in the radical treatment apparatus, when oxygen radicals aresupplied to the wafer W, the oxygen radicals 102 are bonded to thedangling bonds 100 of the SiO₂ molecules on the surface of the wafer Was shown in FIG. 6. Then, as shown in FIG. 7, the oxygen radicals 102bonded to the surface of the wafer W react with surrounding H₂O (water)molecule 103 and become OH groups 101. As a result, the entire surfaceof the SiO₂ film 1 is uniformly hydrophilized, and the OH groups 101 aredistributed.

Next, in the COR treatment apparatus, HF gas and NH₃ gas are supplied.Since the HF molecules 104 and the NH₃ molecules 105 are easily adsorbedto the OH groups 101, the HF molecules 104 and the NH₃ molecules 105tend to be adsorbed to the vicinity of the OH groups 101 on the surfaceof the wafer W.

Upon completion of the annealing and the CMP, the OH groups 101 on thesurface of the wafer W are distributed sparsely as shown in FIG. 5.Therefore, when the HF gas and the NH₃ gas are supplied, the HFmolecules 104 and the NH₃ molecules 105 are locally adsorbed to portionswhere the OH groups 101 are bonded on the surface of the wafer W. Inthis regard, by supplying oxygen radicals to the surface of the SiO₂film 1 and uniformly distributing the OH groups 101 over the entiresurface, the HF molecules 104 and the NH₃ molecules 105 are uniformlydistributed as shown in FIG. 8.

As described above, the HF molecules 104 and the NH₃ molecules 105 reactwith the SiO₂ film 1, and the reaction products are sublimated byheating and the SiO₂ film 1 is removed by etching. At this time, if theHF molecules 104 and the NH₃ molecules 105 are locally adhered to thesurface of the SiO₂ film 1, the etching is promoted at the portionswhere the HF molecules 104 and the NH₃ molecules 105 are locallyadhered, which makes the etching non-uniform. Therefore, when etching isperformed to leave the SiO₂ film 1 in the grooves 12, the roughness onthe surface (surface roughness) of the wafer W after the etchingdeteriorates.

In this regard, the SiO₂ film 1 is uniformly etched by uniformlyhydrophilizing the surface of the SiO₂ film 1 and allowing the HFmolecules 104 and the NH₃ molecules 105 to be uniformly adsorbed.Accordingly, it is presumed that the deterioration of the roughness onthe surface (surface roughness) of the SiO₂ film 1 after the etching issuppressed when the etching is performed to leave the SiO₂ film 1.

Next, the radical treatment apparatus for performing a process ofirradiating the oxygen radical 102 to the surface of the wafer W will bedescribed. As shown in FIG. 9, the radical treatment apparatus includesa grounded processing chamber 20 made of, e.g., stainless steel, and acylindrical mounting table 21 for mounting thereon the wafer W isprovided in the processing chamber 20. For example, a temperaturecontrol flow path 39 is formed in the mounting table 21, and atemperature of the wafer W heated by plasma to be described later isadjusted to, e.g., 10° C. to 120° C. The illustration of lifting pinsfor transferring the wafer W and a lifting mechanism for raising andlowering the lifting pins is omitted. A gas exhaust port 22 is formed ata bottom surface of the processing chamber 20. A gas exhaust line 34 inwhich a pressure control valve 35 and an opening/closing valve 36 areinstalled is connected to the gas exhaust port 22. A gas is exhaustedthrough a vacuum evacuation unit 37. A loading/unloading port 30 forloading/unloading the wafer W is provided on a sidewall of theprocessing chamber 20. A gate valve 70 is provided at theloading/unloading port 30.

A dielectric window 23, e.g., a quartz plate or the like, is provided ata ceiling plate portion of the processing chamber 20 to face the wafer Wmounted on the mounting table 21. A high frequency antenna 24 formed ofa spiral planar coil is mounted on an upper surface of the dielectricwindow 23. A high frequency power supply 26 for outputting a highfrequency power of, e.g., 200 W to 1200 W, is connected to a central endportion of the coil-shaped high frequency antenna 24 through a matchingunit 25. An outer peripheral end portion of the high frequency antenna24 is grounded.

An ion trap plate 32, e.g., a punching plate made of a conductivemember, having through holes 33 is provided below a plurality of gassupply ports 27 and above the mounting table 21 and theloading/unloading port 30 in the processing chamber 20. The ion trapplate 32 adsorbs and traps ions contained in the plasma passing throughthe through holes 33.

The gas supply ports 27 opened toward the inside of the processingchamber 20 and configured to supply O₂ gas and Ar gas to a space betweenthe ion trap plate 32 and the dielectric window 23 are provided on thesidewall of the processing chamber 20. A gas supply line 28 is connectedto the gas supply ports 27. The gas supply line 28 is connected to an O₂gas supply source 29 through a valve V11 and a flow rate controller M11and also connected to an Ar gas supply source 38 for supplying Ar gas asan additional gas through a valve V12 and a flow rate controller M12.

In the above-described radical treatment apparatus, the wafer W ismounted on the mounting table 21 and, then, a pressure in the processingchamber 20 is set within a range from 13.3 Pa to 133 Pa (100 mTorr to1000 mTorr), e.g., 20 Pa. O₂ gas is supplied at a flow rate of 100 sccmto 800 sccm. Ar gas as an additional gas is supplied at a flow rate of50 sccm to 800 sccm. Accordingly, O₂ gas and Ar gas fill a space betweenthe ion trap plate 32 and the dielectric window 23 in the processingchamber 20. Thereafter, the high frequency power of 200 W to 1200 W isapplied from the high frequency power supply 26 to the high frequencyantenna. As a consequence, O₂ gas and Ar gas in the space between theion trap plate 32 and the dielectric window 23 are excited and turnedinto plasma. The plasma is moved downward. When the plasma passesthrough the ion trap plate 32, ions contained in the plasma are removed,and oxygen radicals become main active species to be supplied to thewafer W. Then, the wafer W is exposed to the oxygen radicals for, e.g.,10 sec to 180 sec. At this time, the wafer W is set to about 10° C. to120° C. Accordingly, the entire surface of the SiO₂ film 1 ishydrophilized as described above.

Next, an apparatus for supplying oxygen radicals to the wafer W andetching the SiO₂ film 1, i.e., a COR treatment apparatus in thisexample, will be described. As shown in FIG. 10, the COR treatmentapparatus includes a processing chamber 40 that is a vacuum chamber. Acylindrical mounting table 42 for mounting the wafer W thereon isprovided in the processing chamber 40. A heater 56 forming a heatingunit is provided in the mounting table 42. Three through-holes 57 areformed in the mounting table 42 at an equal interval in acircumferential direction. Lifting pins 51 are inserted into thethrough-holes 57. The lifting pins 51 are movable up and down by alifting mechanism 52 provided below the processing chamber 40. The waferW is delivered to the mounting table 42 by cooperation with the liftingpins 51 and an external transfer mechanism. A loading/unloading port 53for loading/unloading the wafer W is provided on a sidewall of theprocessing chamber 20, and a gate valve 70 is provided at theloading/unloading port 30.

A gas shower head 43 is provided at an upper portion of the processingchamber 40. The gas shower head 43 is configured to supply a gasdispersed in a dispersion space 44 provided therein toward the wafer Wthrough a diffusion plate 60. A gas supply passage 59 is formed tocommunicate with the dispersion space 44. An upstream end portion of thegas supply passage 59 is branched into two parts connected to gas supplylines 45 and 46, respectively. In FIG. 10, a reference numeral 58denotes a diffusion portion for diffusing the gas supplied from the gassupply passage 59 into the distribution space 44.

An upstream side of the gas supply line 45 is branched and connected toan ammonia (NH₃) gas supply source 47 and an N₂ gas supply source 48 forsupplying nitrogen (N₂) gas as a dilution gas (carrier gas). An upstreamside of the gas supply line 46 is branched and connected to an HF gassupply source 49 and an Ar gas supply source 50 for supplying argon (Ar)gas as a dilution gas (carrier gas). In FIG. 10, notations V1 to V4denote valves, and notations M1 to M4 dentate flow rate controllers. Agas exhaust port 41 for exhausting an atmosphere in the processingchamber 40 is provided at a bottom surface of the processing chamber 40.A gas exhaust line 71 is connected to the gas exhaust port 41. A gas isexhausted through a vacuum evacuation unit 74. In FIG. 10, referencenumerals 72 and 73 denote a pressure control valve and anopening/closing valve, respectively.

In the above-described COR treatment apparatus, the wafer W mounted onthe mounting table 42 is heated to 115° C. A pressure in the processingchamber 40 is set to 250 Pa (1.88 Torr). A gas containing HF gas and NH₃gas is supplied toward the wafer W. Accordingly, as described above, theSiO₂ film 1 formed on the wafer W reacts with the HF gas and the NH₃ gasto generate the reaction product 106, and the reaction product 106 issublimated and removed by heating.

The radical treatment apparatus and the COR treatment apparatus areprovided at, e.g., a vacuum processing apparatus of a multi-chambersystem. As shown in FIG. 11, the vacuum processing apparatus includes ahorizontally elongated normal pressure transfer chamber 62 in which anormal pressure atmosphere is set by, e.g., N₂ gas. Load ports 61 fordelivering wafers W to and from carriers C accommodating wafers W areinstalled in front of the normal pressure transfer chamber 62. Areference numeral 67 in FIG. 11 denotes an opening/closing door providedon a front wall of the normal pressure transfer chamber 62. A transferarm 65 for transferring the wafer W is provided in the normal pressuretransfer chamber 62. An alignment chamber 66 for adjusting orientationand eccentricity of the wafer W is provided on a left sidewall whenviewed from the load port 61 side of the normal pressure transferchamber 62.

On the side of the normal pressure transfer chamber 62 opposite to theload port 61, two load-lock chambers 63 of which inner atmosphere isswitched between a normal pressure atmosphere and a vacuum atmosphere ina state where the wafer W is on standby are arranged side by side. Avacuum transfer chamber 64 is provided behind the load-lock chambers 63when viewed from the normal pressure transfer chamber 62 side. Thevacuum transfer chamber 64 is connected to the load-lock chambers 63, aradical treatment apparatus 8, and a COR processing device 9 throughgate valves 70. A transfer arm 69 is provided in the vacuum transferchamber 64 and transfers the wafer W between the load-lock chambers 63,the radical treatment apparatus 8, and the COR treatment apparatus 9.

The vacuum processing apparatus includes a control unit 90, e.g., acomputer. The control unit 90 includes a program, a memory, and a dataprocessing unit having a CPU. The program has a group of commands(steps) so that each step of executing, e.g., radical treatment oretching, can be executed by outputting control signals to the respectivecomponents of the vacuum processing apparatus from the control unit 90.This program is stored in a storage unit such as a computer storagemedium, e.g., a flexible disk, a compact disk, a hard disk, an MO(magneto-optical disk) or the like, and installed in the control unit90.

When a transfer carrier C accommodating the wafer W having a surfacestructure shown in FIG. 1, for example, is loaded onto the load port 61of the vacuum processing apparatus, the wafer W is taken out from thetransfer carrier C and loaded into the alignment chamber 66 via thenormal pressure transfer chamber 62 and subjected to alignment. Then,the wafer W is transferred to the vacuum transfer chamber 64 via theload-lock chamber 63. Next, the wafer is transferred to the radicaltreatment apparatus 8 by the transfer arm 69 and subjected to theabove-described radical processing. Then, the wafer W is transferred tothe COR treatment apparatus 9 by the transfer arm 69 and subjected tothe above-described etching using the COR method. In this manner, thewafer W having the etched SiO₂ film is transferred to the load-lockchamber 63 in a vacuum atmosphere by the second transfer arm 69.Thereafter, the atmosphere in the load-lock chamber is switched to theatmospheric atmosphere, and the wafer W is returned to, e.g., theoriginal carrier C, by the transfer arm 65.

The wafer W unloaded from the COR treatment apparatus 9 may be loadedinto a heating processing chamber connected to the vacuum transferchamber 64 and heated therein at a temperature higher than the heatingtemperature in the COR treatment apparatus 9 to reliably sublimate thereaction product 106.

In accordance with the above-described embodiment, when the SiO₂ film 1formed on the surface of the wafer W is etched to some extent that hasnot yet reached an underlying layer, the surface of the SiO₂ film 1 isirradiated with O₂ radicals and hydrophilized. Then, the SiO₂ film 1 isetched by NH₃ gas and HF gas. Therefore, NH₃ gas and HF gas areuniformly adsorbed on the surface of the SiO₂ film 1. Accordingly, thesurface of the SiO₂ film 1 is uniformly etched, and the surfaceroughness (roughness) is improved.

As for a method for supplying oxygen radicals to the surface of the SiO₂film 1, there may be employed a method for supplying a plasma obtainedby activating O₃ (ozone) gas or a gaseous mixture of O₂ gas and O₃ gas,instead of activating O₂ gas, to the wafer W through the ion trap plate32. In addition, as for a method for hydrophilizing the surface of theSiO₂ film 1, there may be employed a method using a so-called softplasma containing active species of oxygen having a low electrontemperature without the ion trap treatment of the plasma. As for ahydrophilization method, it is possible to use a method for supplyingwater vapor to the surface of the wafer W shown in FIG. 1, other thanthe plasma supply.

In the case of etching the SiO₂ film 1, in the COR treatment apparatusshown in FIG. 10, NH₃ gas and HF gas are supplied to the wafer W and thereaction product 106 is generated by the reaction between the SiO₂ film1 and the NH₃ gas and the HF gas. Then, the wafer W unloaded from theCOR treatment apparatus may be transferred to a heating apparatus, andthe reaction product 106 may be sublimated by heating the wafer W.

The SiO₂ film 1 can be etched by using a processing gas containing acompound of nitrogen, hydrogen and fluorine, e.g., ammonium fluoride(NH₄F) gas. In this case as well, the gas reacts with the SiO₂ film 1 togenerate (NH₄)₂SiF₆. Therefore, in the case of etching the wafer Whaving the SiO₂ film 1, ammonium fluoride (NH₄F) (or NH₄FHF) gas may besupplied. The processing gas may be a gaseous mixture of NH₃ gas, HF gasand NH₄F gas (or NH₄ FHF).

The method of etching the SiO₂ film 1 is not limited to the COR, andplasma etching may be performed. For example, it is possible to generateplasma of a processing gas containing NF₃ gas and NH₃ gas or plasma of aprocessing gas containing HF gas and NH₃ gas and then supply the plasmato the wafer W through the ion trap plate 32. As for a gas used togetherwith NH₃ gas in the etching, a gas containing halogen other than F, suchas HBr gas or the like, may be used. Further, ethanol (C₂H₅OH) or water(H₂O) may be used instead of NH₃ gas.

Even when the SiO₂ film 1 is completely removed and the underlying layeris exposed, the roughness may be transferred to the surface of theunderlying layer at the time of etching the SiO₂ film 1. Therefore, thepresent invention is effective even in the case of completely removingthe SiO₂ film 1.

TEST EXAMPLES

In order to verify the effect of the present invention, the wafer W wasetched and the uniformity of the surface was evaluated.

In a test example, an SiO₂ film was formed by CVD using, e.g., anorganic raw material gas and an oxidizing gas, on the surface of a waferW and, then, annealing was performed by heating the wafer W to 400° C.to 1000° C. while performing purging using N₂ gas in a vacuumatmosphere. A sample shown in FIG. 1 was obtained by polishing thesurface by CMP. As in the above-described embodiment, oxygen radicalswere supplied for 180 sec to the sample by the radical treatmentapparatus shown in FIG. 9. Then, the etching using HF gas and NH₃ gaswas performed by the COR treatment apparatus shown in FIG. 10, and theSiO₂ film 1 was etched to some extent. In a comparative example, thesame treatment as that in the test example was performed except thatoxygen radicals were not irradiated.

In each of the test example and the comparative example, the roughness(root mean square roughness) of the surface of the wafer W after theetching was measured. As a reference example, the SiO₂ film 1 was formedby CVD and, then, the annealing and the polishing using CMP wereperformed. Then, the roughness (root mean square roughness) of thesurface of the wafer W was measured.

The root mean square roughness (hereinafter, referred to as “averageroughness RMS”) is obtained by subtracting a reference length e from aroughness curve in a direction of an average line, setting the directionof the average line of the reference length e to the X-axis and adirection of longitudinal magnification to the Y-axis and summing theroot mean square of the deviation from an average line of the referencelength e to a measurement curve. When the roughness curve is expressedby y=f(x), RMS can be obtained by the following equation.

${RMS} = \sqrt{\frac{1}{\ell}{\int_{c}^{\prime}{{f^{\prime}(x)}{dx}}}}$

A sample of the test example, a sample of the comparative example and asample of the reference example were prepared, and the average roughnessRMS in each sample was measured.

FIG. 12 shows the results thereof, i.e., the average surface roughnessesRMS in the test example, the comparative example and the referenceexample. An error line in FIG. 12 shows system deviation at the time ofAFM (Atomic Force Microscope) measurement. FIG. 13 shows images of thesurface of the wafer W in the reference example, the comparativeexample, and the test example. As shown in FIG. 12, the average surfaceroughness RMS of the surface of the wafer W in the reference example was0.298; the RMS in the comparative example was 3.108; and the RMS in thetest example was 1.313. As shown in FIG. 12, irregularities were hardlyobserved in the reference example; large irregularities were observed inthe comparative example; and irregularities in the test example weresmaller than those in the comparative example.

According to the result, the surface roughness deteriorates by polishingthe SiO₂ film 1 by CMP and etching the SiO₂ film 1 to some extent byusing HF gas and NH₃ gas. However, the roughness deterioration of thesurface is improved by 58% by irradiating the surface of the SiO₂ film 1with oxygen radicals before the etching is performed by using HF gas andNH₃ gas.

Therefore, in accordance with the present invention, when the surface ofthe SiO₂ film 1 is etched, the deterioration of the surface roughnesscan be suppressed.

What is claimed is:
 1. A substrate processing method comprising: etchinga part of a silicon oxide layer formed on a surface of a substrate toleave a remaining part of the silicon oxide layer on the surface of thesubstrate, said etching including: a first step of hydrophilizing asurface of the silicon oxide layer on which dangling bonds of SiO₂molecules are arranged; and a second step of etching the remaining partof the silicon oxide layer by supplying a halogen-containing gas to thesubstrate and sublimating a reaction product generated by reactionbetween the halogen-containing gas and the silicon oxide layer, whereinin the first step, a plasma passes through an ion trap member having aplurality of gas through holes to generate oxygen radicals and theoxygen radicals are bonded to the dangling bonds of SiO₂ molecules bysupplying the oxygen radicals to the surface of the silicon oxide layer,and wherein said etching the part of the silicon oxide layer forms agroove in the substrate, the remaining part of the silicon oxide layerbeing disposed in the groove.
 2. The substrate processing method ofclaim 1, wherein the plasma is generated by activating at least one ofoxygen gas and ozone gas.
 3. The substrate processing method of claim 1,wherein the second step is a step of exposing the surface of the siliconoxide layer to at least one of a processing gas containing a hydrogenfluoride gas and an ammonia gas and a processing gas containing acompound of nitrogen, hydrogen and fluorine.
 4. The substrate processingmethod of claim 1, wherein in the second step, the silicon oxide layeris etched by plasma obtained by activating a gaseous mixture of anitrogen trifluoride gas or a hydrogen fluoride gas and an ammonia gas.5. The substrate processing method of claim 1, wherein the silicon oxidelayer is deposited by reaction between a raw material gas and anoxidizing gas.
 6. The substrate processing method of claim 1, wherein inthe first step, the substrate is exposed to the oxygen radicals for 10to 180 seconds while the temperature of the substrate is 10 to 120° C.7. The substrate processing method of claim 1, wherein, after the partof the silicon oxide layer is etched to leave the remaining part of thesilicon oxide layer on the surface of the substrate, the supplying ofthe halogen-containing gas is stopped and a purge gas is supplied to thesubstrate to stop the etching.
 8. The substrate processing method ofclaim 1, wherein the plasma includes ions and the ions are absorbed inthe ion trap member as the plasma passes through the ion trap membersuch that the plasma that exists the ion trap member lacks the ions. 9.The substrate processing method of claim 1, wherein in the first stepthe surface of the silicon oxide layer is uniformly hydrophilized in itsentirety.
 10. A substrate processing method comprising: etching a partof a silicon oxide layer formed on a surface of a substrate to leave aremaining part of the silicon oxide layer on the surface of thesubstrate, said etching including: a first step of hydrophilizing asurface of the silicon oxide layer on which dangling bonds of SiO₂molecules are arranged; and a second step of etching the part of thesilicon oxide layer by supplying a halogen-containing gas to thesubstrate and sublimating a reaction product generated by reactionbetween the halogen-containing gas and the silicon oxide layer, whereinin the first step, a plasma passes through an ion trap member having aplurality of gas through holes to generate oxygen radicals and theoxygen radicals are bonded to the dangling bonds of SiO₂ molecules bysupplying the oxygen radicals to the surface of the silicon oxide layer,wherein the method further comprises: before said hydrophilizing thesurface of the silicon oxide layer, annealing the silicon oxide layer;and polishing and planarizing the silicon oxide layer.